#include <stdio.h>
#include <stdlib.h>
#include <math.h>

float cal_std_dev(float *, int);

int main()
{
	float list[20];
	int num = 0;
	do
	{
		scanf("%f", &list[num]);
		num++;
	}while(getchar() != '\n');
	printf("std_dev:%f\n", cal_std_dev(list, num));
	return 0;
}
 
float cal_std_dev(float data[], int num)
{
    float sum = 0.0, mean, std_dev = 0.0;
 
    int i;
 
    for(i=0; i<num; ++i)
    {
        sum += data[i];
    }
 
    mean = sum/num;
    printf("mean:%f\n", mean);
 
    for(i=0; i<num; ++i)
        std_dev += pow(data[i] - mean, 2);
 
    return sqrt(std_dev/num);
}

